Communication apparatus and communication method

ABSTRACT

The efficiency of signal transmission is improved. A communication apparatus includes a memory unit, a communication control unit, and an updating unit. A retransmission interval value is stored in the memory unit. The communication control unit transmits a first signal and receives a response signal corresponding to the first signal from a receiver. If the received response signal is a negative response signal, the first signal is retransmitted at a time interval longer than or equal to the retransmission interval value stored in the memory unit, from the transmission of the first signal. The updating unit updates the retransmission interval value stored in the memory unit, according to a time from the transmission of the first signal to the reception of the positive response signal corresponding to the first signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2016-181854 filed onSep. 16, 2016 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

The present invention relates to a communication apparatus and acommunication method.

BACKGROUND

As a known technique for increasing the reliability of signaltransmission of the related art, for example, retransmission control isdisclosed in Japanese Unexamined Patent Application Publication No.2004-260562.

SUMMARY

Regarding signal transmission, transmission efficiency is alsorequested.

Considering requests on transmission efficiency, the present inventorshave found the following problem:

In the retransmission control disclosed in Japanese Unexamined PatentApplication Publication No. 2004-260562, retransmission intervals arefixed values and thus retransmission may be repeated many times in, forexample, heavy traffic on a communication path between a transmitter anda receiver. Thus, the band of the communication path may be occupied byretransmission so as to reduce transmission efficiency.

Other problems and new features will be clarified by a description ofthe present specification and the accompanying drawings.

According to an embodiment, a communication apparatus transmits a firstsignal and receives a response signal corresponding to the first signalfrom a receiver. If the communication apparatus receives a negativeresponse signal, the first signal is retransmitted at a time intervallonger than or equal to a set retransmission interval value after thetransmission of the first signal, and the set retransmission intervalvalue is updated according to a time from the transmission of the firstsignal to the reception of response signal.

The embodiment can increase the efficiency of signal transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a communication system according to a firstembodiment;

FIG. 2 is a block diagram showing an example of a communication controlunit according to the first embodiment;

FIG. 3 is a flowchart showing an example of operation of a transmissionnode according to the first embodiment;

FIG. 4 is an explanatory drawing showing an operation example of thecommunication system according to the first embodiment;

FIG. 5 is an explanatory drawing showing another application example ofthe communication system according to the first embodiment;

FIG. 6 is a block diagram showing an example of the communicationcontrol unit of a transmission node according to a second embodiment;

FIG. 7 is a flowchart showing an example of the operations thetransmission node according to the second embodiment;

FIG. 8 is a block diagram showing an example of the communicationcontrol unit of a transmission node according to a third embodiment;

FIG. 9 is a flowchart showing an example of the operations thetransmission node according to the third embodiment; and

FIG. 10 is a sequence showing an example of the operations of acommunication system according to the third embodiment.

DETAILED DESCRIPTION

Embodiments will be described below with reference to the accompanyingdrawings. The same elements are indicated by the same reference symbolsand a redundant explanation thereof is omitted.

First Embodiment Outline of a Communication System

FIG. 1 shows an example of a communication system according to a firstembodiment. In FIG. 1, a communication system 1 includes communicationapparatuses 10 and 20, interfaces 30 and 40, and a transmission line P1.

The communication apparatus 10 transmits a signal to be transmitted tothe communication apparatus 20 on the other end. In other words, thecommunication apparatus 10 operates as a “transmission node” in thisconfiguration. The signal transmitted from the communication apparatus10 reaches the communication apparatus 20 through the interface 30, thetransmission line P1, and the interface 40. In this case, thecommunication apparatus 10 and the communication apparatus 20 may havewired or wireless coupling. In the case of wired coupling, thetransmission line P1 may be, for example, a communication line and theinterfaces 30 and 40 may be, for example, connectors. In the case ofwireless coupling, the transmission line P1 may be, for example, a radiotransmission line and the interfaces 30 and 40 may be, for example,radio antennas.

The communication apparatus 20 receives the signal transmitted from thecommunication apparatus 10. In other words, the communication apparatus20 operates as a “reception node” in this configuration. When receivingthe signal transmitted from the communication apparatus 10, thecommunication apparatus 20 transmits a response signal to thecommunication apparatus 10. In this case, the response signal is apositive response signal or a negative response signal. For example, apositive response signal may be transmitted when the signal transmittedfrom the communication apparatus 10 can be correctly received, whereas anegative response signal may be transmitted when the signal transmittedfrom the communication apparatus 10 cannot be correctly received. Inother words, the positive response signal and the negative responsesignal may be an ACK signal and a NACK signal, respectively. Forexample, if the signal transmitted from the communication apparatus 10is a request signal indicating a request to the communication apparatus20, the positive response signal may be transmitted when thecommunication apparatus 20 accepts the request, whereas the negativeresponse signal may be transmitted when the request is declined. In thefollowing explanation, the positive response signal and the negativeresponse signal will be described as an ACK (ACKnowledgement) signal anda NACK (Negative Acknowledgement) signal, respectively, unless otherwisespecified.

When receiving the positive response signal that corresponds to thesignal (will be referred to as “first signal”) transmitted by thecommunication apparatus 10 and is transmitted from the communicationapparatus 20, the communication apparatus 10 may transmit a secondsignal to the communication apparatus 20 subsequently to the firstsignal after a predetermined time from the reception of the positiveresponse signal. In this case, it is assumed that the first signal andthe second signal are a series of packet signals.

When receiving the negative response signal that corresponds to thesignal (will be referred to as “first signal”) transmitted by thecommunication apparatus 10 and is transmitted from the communicationapparatus 20, the communication apparatus 10 retransmits the firstsignal to the communication apparatus 20.

In this case, the communication apparatus 10 retransmits the firstsignal at a time interval longer than or equal to “set retransmissioninterval value” after the transmission of the first signal. Moreover,the communication apparatus 10 updates “set retransmission intervalvalue” based on a time from the transmission of the first signal to thereception of the positive response signal corresponding to the firstsignal. Thus, at the retransmission of the second signal transmittedafter the first signal, the communication apparatus 10 can retransmitthe signal according to a retransmission interval value adjusted basedon the actual transmission time of the first signal. This can preventtransmission efficiency from being reduced by repeatedly retransmittingthe same signal so as to occupy the band of the transmission line P1. Inother words, the signal can be transmitted with higher efficiency.

Configuration Example of the Transmission Node

As described above, the communication apparatus 10 operates as atransmission node and thus the configuration of the communicationapparatus 10 will be discussed below. In FIG. 1, the communicationapparatus 10 includes a transmitting unit 11, a communication controlunit 12, a receiving unit 13, a memory unit 14, and an updating unit 15.

The transmitting unit 11 receives a signal to be transmitted. Whenreceiving a transmission instruction from the communication control unit12, the transmitting unit 11 performs a predetermined transmittingoperation on the signal to be transmitted, and then sends the signal tothe interface 30. Thus, the signal to be transmitted is transmitted tothe communication apparatus 20 serving as a receiver. At this point, thetransmitting unit 11 temporarily stores the transmitted signal inpreparation for retransmission. The stored signal to be transmitted(will be referred to as “first signal”) is deleted by the transmittingunit 11 when a transmission instruction on a signal (will be referred toas “second signal”) to be transmitted subsequently to the first signalis received by the transmitting unit 11 from the communication controlunit 12.

When receiving a retransmission instruction from the communicationcontrol unit 12, the transmitting unit 11 transmits the stored signal tothe interface 30 to retransmit the stored signal indicated by theretransmission instruction.

The receiving unit 13 receives the response signal transmitted from thecommunication apparatus 20 and then outputs the received response signalto the communication control unit 12.

When receiving the first signal to be transmitted (will be referred toas “first signal”), the communication control unit 12 transmits atransmission instruction on the first signal to the transmitting unit11. Thus, the first signal is transmitted from the transmitting unit 11.When receiving the second signal subsequent to the first thecommunication control unit 12 receives the positive response signal forthe first signal and then outputs the transmission instruction on thesecond signal the transmitting unit 11. In this configuration, whenreceiving the positive response signal, the communication control unit12 outputs “updated value” of the retransmission interval value to theupdating unit 15. “Updated value” is based on a time from thetransmission of the first signal to the reception of the positiveresponse signal corresponding to the first signal. Moreover, if thepositive response signal corresponding to the second signal is received,“updated value” outputted from the communication control unit 12 isbased on a time from the transmission of the second signal to thereception of the positive response signal corresponding to the secondsignal. The “updated value” will be specifically described later.

If the response signal received from the receiving unit 13 is thenegative response signal, the communication control unit 12 outputs atransmission instruction to the transmitting unit 11 at a time intervallonger than or equal to the retransmission interval value (i.e., the setretransmission interval value) held (stored) in the memory unit 14,after the previous transmission (including retransmission) of the signalto be transmitted for the response signal. In other words, a signal tobe transmitted is retransmitted at substantially the same interval as aretransmission interval value stored in the memory unit 14, after theprevious transmission.

The updating unit 15 receives the updated value outputted from thecommunication control unit 12 and updates, according to the receivedupdated value, the retransmission interval value stored in the memoryunit 14. Specifically, the updating unit 15 updates the retransmissioninterval value based on a time from the transmission of the first signalto the reception of the positive response signal corresponding to thefirst signal. After that, the communication control unit 12 refers tothe updated retransmission interval value.

FIG. 2 is a block diagram showing an example of the communicationcontrol unit according to the first embodiment. In FIG. 2, thecommunication control unit 12 includes a communication controlprocessing unit 12A, a timer 12B, a counter 12C, and a calculating unit12D.

After receiving the signal to be transmitted and outputting atransmission instruction on the signal to the transmitting unit 11, thecommunication control processing unit 12A outputs a count instruction tothe timer 12B. The timer 12B starts a time measurement in response tothe count instruction. The timer 12B receives a clear instruction, whichwill be discussed later, and the count instruction from thecommunication control processing unit 12A so as to repeatedly measure atime corresponding to the set retransmission interval value.

Moreover, the communication control processing unit 12A refers to thetimer value (i.e., a time measured value) of the timer 12B with apredetermined period and refers to the set retransmission interval valuestored in the memory unit 14 with the predetermined period.Subsequently, when the time measured value of the timer 12B reaches theset retransmission interval value, the communication control processingunit 12A outputs the clear instruction to the timer 12B to reset thetime measured value of the timer 12B. After that, the communicationcontrol processing unit 12A outputs the count instruction. At thispoint, the communication control processing unit 12A outputs anincrement instruction to the counter 12C. In response to the incrementinstruction, the counter 12C increments a count value by one. In otherwords, the counter 12C counts the number of time intervals, each beingcounted by the timer 12B and corresponding to the set retransmissioninterval value.

When receiving the negative response signal from the receiving unit 13,the communication control processing unit 12A compares the time measuredvalue of the timer 12B and the set retransmission interval value.Subsequently, the communication control processing unit 12A outputs theretransmission instruction to the transmitting unit 11 when the timemeasured value reaches the set retransmission interval value. Thus, thesignal is retransmitted at a time interval corresponding to the setretransmission interval value.

When receiving the positive response signal from the receiving unit 13,the communication control processing unit 12A outputs a calculationinstruction to the calculating unit 12D. The calculating unit 12Dcalculates “updated value” in response to the calculation instruction.Subsequently, the communication control processing unit 12A outputs theclear instruction to the timer 12B and the counter 12C at the end ofreference to the timer 12B and the counter 12C by the calculating unit12D.

The calculating unit 12D acquires the timer value of the timer 12B andthe count value of the counter 12C when receiving the calculationinstruction from the communication control processing unit 12A. Thecalculating unit 12D calculates “updated value” according to theacquired timer value and count value.

For example, the calculating unit 12D calculates an updated valueaccording to the following equation (1):

Updated value=timer value+set retransmission interval value×countvalue  (1)

Subsequently, the calculating unit 12D outputs the calculated updatedvalue to the updating unit 15.

Configuration Example of the Reception Node

As described above, the communication apparatus 20 operates as areception node and thus the configuration of the communication apparatus20 will be discussed below. In FIG. 1, the communication apparatus 20includes a receiving unit 21, a control unit 22, and a transmitting unit23.

The receiving unit 21 receives the signal transmitted from thecommunication apparatus 10 and outputs the received signal to thecontrol unit 22.

The control unit 22 outputs, to the transmitting unit 23, the responsesignal corresponding to the received signal from the receiving unit 21.As described above, the response signal is a positive response signal ora negative response signal.

The transmitting unit 23 transmits the response signal received from thecontrol unit 22, to the communication apparatus 10.

Operation Example of the Communication System

An operation example of the communication system 1 configured thusaccording to the first embodiment will be described below. FIG. 3 is aflowchart showing an example of an operation of the transmission nodeaccording to the first embodiment. In this case, an example of thesignal to be transmitted is a series of packets.

The communication control unit 12 stores the initial value of theretransmission interval value in the memory unit 14, allowing thesetting of the initial value of the retransmission interval value (StepS101).

Subsequently, the communication control unit 12 outputs the transmissioninstruction to the transmitting unit 11 to transmit a packet (StepS102).

The communication control unit 12 then starts the timer 12B to start atime measurement (Step S103).

After that, the communication control unit 12 decides whether thepositive response signal corresponding to the packet transmitted in stepS102 has been received or not (Step S104). If the positive responsesignal has not been received (Step S104 NO), the communication controlunit 12 decides whether the negative response signal has been receivedor not (Step S105). In other words, the decisions in step S104 and stepS105 are repeated until the positive response signal or the negativeresponse signal is received.

If the negative response signal is received (Step S105 YES), thecommunication control unit 12 decides whether the measured value of thetimer 12B has reached the set retransmission interval value or not (StepS106). The decision in step S106 is repeated until the measured value ofthe timer 12B reaches the set retransmission interval value (Step S106NO).

If the measured value of the timer 12B has reached the setretransmission interval value (Step S106 YES), the communication controlunit 12 increments the count value of the counter 12C (Step S107) andclears the timer value of the timer 12B (Step S108). The communicationcontrol unit 12 then outputs the retransmission instruction to thetransmitting unit 11 to retransmit the packet (Step S109). After that,the processing step returns to step S103.

If the positive response signal has been received (Step S104 YES), thecommunication control unit 12 calculates “updated value” (Step S110)Subsequently, the updating unit 15 updates the set retransmissioninterval value stored in the memory unit 14, according to “updatedvalue” calculated by the communication control unit 12 (Step S111). Thecommunication control unit 12 then clears the measured value of thetimer 12B (Step S112) and clears the count value of the counter 12C(Step S113).

The processing steps from step S102 to step S113 are repeated untilafter the transmission of a series of packets to be transmitted (StepS114 NO). After the transmission of the series of packets to betransmitted (Step S114 YES), a processing flow in FIG. 3 is ended.

A specific example of an update of the retransmission interval valuewill be described below. FIG. 4 is an explanatory drawing showing theoperation example of the communication system according to the firstembodiment.

In FIG. 4, a section A, a section B, a section C, and a section Dindicate sections for correctly receiving a packet 1, a packet 2, apacket 3, and a packet 4 in the end by the communication apparatus 20.In the first section A, the set retransmission interval value is set atan initial value T0.

The communication apparatus 10 transmits the packet 1 to thecommunication apparatus 20 (Step S201). At this point, the measurementof the timer 12B is started. The communication apparatus 20 thentransmits a positive response signal for the packet 1 (Step S202). Whenreceiving the positive response signal, the communication apparatus 10terminates the measurement of the timer 12B. At this point, the timer12B has a measured value t1 that is used as a set retransmissioninterval value T1 of the subsequent section B.

The communication apparatus 10 has received the positive response signalfor the packet 1 and thus transmits the subsequent packet 2 to thecommunication apparatus 20 (Step S203). At this point, the measurementof the timer 12B is started. The communication apparatus 20 thentransmits the negative response signal corresponding to the packet 2 tothe communication apparatus 10 (Step S204). When receiving the negativeresponse the communication apparatus 10 retransmits the packet 2.However, the packet 2 is retransmitted after a lapse of the setretransmission interval value T1 or more from the previous transmissionof the packet 2. Thus, the communication apparatus 10 retransmits thepacket 2 after a lapse of the set retransmission interval value T1 fromthe transmission of the packet 2 in step S203 (Step S205). At thispoint, the measured value of the timer 12B is cleared and then the timer12B restarts a measurement; meanwhile, the count value of the counter12C is incremented from “0” to “1”. Subsequently, the communicationapparatus 20 transmits, to the communication apparatus 10, the negativeresponse signal corresponding to the packet 2 retransmitted in step S205(Step S206). The communication apparatus 10 then retransmits the packet2 for the second time after a lapse of the set retransmission intervalvalue T1 from the first retransmission of the packet 2 (Step S207). Atthis point, the measured value of the timer 12B is cleared and then thetimer 12B restarts a measurement; meanwhile, the count value of thecounter 12C is further incremented from “1” to “2”. Subsequently, thecommunication apparatus 20 transmits, to the communication apparatus 10,the positive response signal corresponding to the packet 2 retransmittedin step S207 (Step S208). When receiving the positive response signal,the communication apparatus 10 terminates the measurement of the timer12B. At this point, the timer 12B has a measured value t2 and the countvalue is “2”. Moreover, the current set retransmission interval value is“T1”. These values are substituted in Equation (1), thereby calculatinga set retransmission interval value “T2” in the section C. Thecommunication apparatus 10 then clears the count value of the counter12C.

The communication apparatus 10 has received the positive response signalfor the packet 2 and thus transmits the subsequent packet 3 to thecommunication apparatus 20 (Step S209). At this point, the measurementof the timer 12B is started. The communication apparatus 20 thentransmits the negative response signal corresponding to the packet 3 tothe communication apparatus 10 (Step S210). The communication apparatus10 retransmits the packet 3 after a lapse of the set retransmissioninterval value T2 from the transmission of the packet 3 (Step S211). Atthis point, the measured value of the timer 12B is cleared and then thetimer 12B restarts a measurement; meanwhile, the count value of thecounter 12C is incremented from “0” to “1”. Subsequently, thecommunication apparatus 20 transmits, to the communication apparatus 10,the positive response signal corresponding to the packet 3 retransmittedin step S211 (Step S212). When receiving the positive response signal,the communication apparatus 10 terminates the measurement of the timer12B. At this point, the timer 12B has a measured value t3 and the countvalue is “1”. Moreover, the current set retransmission interval value is“T2”. These values are substituted in Equation (1), thereby calculatinga set retransmission interval value “T3” in the section D. Thecommunication apparatus 10 then clears the count value of the counter12C.

The communication apparatus 10 has received the positive response signalfor the packet 3 and thus transmits the subsequent packet 4 to thecommunication apparatus 20 (Step S213). At this point, the measurementof the timer 12B is started. The communication apparatus 20 thentransmits the positive response signal corresponding to the packet 4 tothe communication apparatus 10 in the first transmission (Step S214).When receiving the positive response signal, the communication apparatus10 terminates the measurement of the timer 12B. At this point, the timer12B has a measured value t4 and the count value is “0”. Moreover, thecurrent set retransmission interval value is “T3”. These values aresubstituted in Equation (1), thereby calculating a set retransmissioninterval value “T4” in the section E where the subsequent packet of thepacket 3 is transmitted.

As described above, in the communication apparatus 10 serving as atransmission node of the first embodiment, the communication controlunit 12 transmits the first signal and receives the response signalcorresponding to the first signal from the receiver (in this case, thecommunication apparatus 20). If the received response signal is anegative response signal, the first signal is retransmitted at a timeinterval longer than or equal to the retransmission interval value,which is stored in the memory unit 14, after the transmission of thefirst signal. Subsequently, the updating unit 15 updates theretransmission interval value, which is stored in the memory unit 14,based on a time from the transmission of the first signal to thereception of the positive response signal corresponding to the firstsignal.

According to the configuration of the communication apparatus 10 servingas a transmission node, the second signal to be transmitted after thefirst signal can be retransmitted according to the retransmissioninterval value adjusted based on the actual transmission time of thefirst signal. In other words, the signal can be retransmitted accordingto a more suitable retransmission interval value for communicationenvironments such as the traffic of the transmission line P1 and thecommunication capacity of the receiver. This can prevent transmissionefficiency from being reduced by repeatedly retransmitting the samesignal so as to occupy the band of the transmission line P1. In otherwords, the signal can be transmitted with higher efficiency.

According to the configuration of the communication apparatus 10, if thepositive response signal can be received in the first transmissionwithout the need for retransmission, the retransmission interval valuecan be adjusted to a smaller value.

Furthermore, the retransmission interval value can be adjusted by thecommunication apparatus 10 alone without being determined between thecommunication apparatus 10 serving as a transmission node and thecommunication apparatus 20 serving as a reception node. Thus, thecommunication apparatus 10 is applicable to various systems. In otherwords, the communication apparatus 10 is highly versatile.

If the positive response signal corresponding to the first signal isreceived, the communication control unit 12 transmits the second signalto the receiver (in this case, the communication apparatus 20)subsequently to the first signal after the predetermined time from thereception of the positive response signal.

The configuration of the communication apparatus 10 can also prevent areduction in transmission efficiency. Specifically, it is assumed thatthe negative response signal is repeated in a certain period during thetransmission of a series of signals to be transmitted. In this case,“signal transmission interval” adjusted as in Japanese Unexamined PatentApplication Publication No. 2004-260562 may cause transmission of theseries of signals at an excessively long signal transmission intervaleven after the positive response signal is repeated. The signaltransmission interval is “an interval from the previous ACK signaltransmission (retransmission) to the current transmission of a signal tobe transmitted, regarding a series of signals to be transmitted.” In thecommunication apparatus 10, the retransmission interval value is updatedbut “signal transmission interval” is not adjusted, thereby preventing areduction in transmission efficiency.

Another Application Example

In the above explanation, the signal to be transmitted is a packet, thepositive response signal is an ACK signal, and the negative responsesignal is a NACK signal. The present invention is not limited to thisapplication. For example, the communication system 1 may be applied to aUSB-compliant system (Universal Serial Bus). Specifically, the techniquemay be applied to the transmission of a transition request (i.e., acontrol signal) to a low-power consumption state that is defined by theUSB 3.1 standard. The USB 3.1 standard will be described below. The USB3.1 standard allows a transition from a normal state “U0” to a low-powerconsumption state “U1/U2” In this case, the signal to be transmitted is,for example, a low-power consumption state transition request(LGO_U1/LGO_U2), the positive response signal is an ACK signal (LAU),and the negative response signal is a NACK signal (LXU). Unlike in theforegoing explanation, the communication apparatus having received LAUtransmits an ACK response (LPMA) to the communication apparatus havingtransmitted LAU, which is specific to the USB standard.

FIG. 5 is an explanatory drawing showing another application example ofthe communication system according to the first embodiment. In FIG. 5,for example, one of the communication apparatus 10 and the communicationapparatus 20 is a host, whereas the other is a device. Moreover, in FIG.5, a section A is a section (sequence) where the communication apparatus10 changed a state used for communications with the communicationapparatus 20, and a section 3 is a section (sequence) where thecommunication apparatus 10 changed a state used for communications withthe communication apparatus 20 at another opportunity after the sectionA. For example, in the section A, the communication apparatus 10 and thecommunication apparatus 20 are coupled to transmit a low-powerconsumption state transition request (LGO_U1/LGO_U2) for the first timeand the retransmission interval value approaches closest to an optimalvalue.

At the beginning of the section A, the power consumption states of thecommunication apparatus 10 and the communication apparatus 20 are bothdesignated as a U0 state. The communication apparatus 10 transmits thelow-power consumption state transition request (LGO_U1/LGO_U2) to thecommunication apparatus 20 (Step S301). At this point, the measurementof the timer 12B is started.

In this step, the communication apparatus 20 having received thelow-power consumption state transition request transmits the NACK signal(LXU) (Step S302).

When receiving the MACK signal (LXU) from the communication apparatus20, the communication apparatus 10 retransmits the low-power consumptionstate transition request after a lapse of the set retransmissioninterval value from the transmission of the low-power consumption statetransition request in step S301 (Step S303). At this point, the measuredvalue of the timer 12B is cleared and then the timer 12B restarts ameasurement; meanwhile, the count value of the counter 12C is furtherincremented.

The communication apparatus 20 having received the retransmittedlow-power consumption state transition request transmits the ACK signal(LAU) to the communication apparatus 10 (Step S304).

When receiving the ACK signal (LAU) from the communication apparatus 20,the communication apparatus 10 acquires the measured value of the timer12B at this point and then terminates the measurement of the timer 12B.Moreover, the communication apparatus 10 acquires the count value of thecounter 12C at this point. Furthermore, the communication apparatus 10acquires the set retransmission interval value at this point. In thiscase, the communication apparatus 10 and the communication apparatus 20are coupled transmit the low-power consumption state transition request(LGO_U1/LGO_U2) for the first time in the section A and thus theacquired set retransmission interval value is equal to the initialvalue. The communication apparatus 10 substitutes these values inEquation (1) to calculate an updated value and then updates the setretransmission interval value according to the calculated updated value.

The communication apparatus 10 then transmits the ACK response (LPMA) tothe communication apparatus 20 (Step S305) and the communicationapparatus 20 receives the ACK response (LPMA). This changes the powerconsumption states of the communication apparatus 10 and thecommunication apparatus 20 to a state indicated by the low-powerconsumption state transition request.

From step S306 to step S310 of the section B, the same processing isperformed as in step S301 to step S305. In this case, a time intervalbetween the transmission of the low-power consumption state transitionrequest in step S306 and the retransmission of the low-power consumptionstate transition request in step S308 is longer than or equal to theretransmission interval value updated in the section A.

If the flowchart of FIG. 3 is applied to the transmission node of thecommunication system 1 compliant with the USB (Universal Serial Bus)standard, the need for processing in step S114 is eliminated and thestep of transmitting the ACK response (LPMA) is added instead. Thisflowchart is implemented in each section (e.g., in the sections A andB). In the first section (e.g., the section A), the retransmissioninterval value is set at the initial value in step S101. In thesubsequent section (e.g., the section B), the retransmission intervalvalue updated in the previous section (e.g., the section A) in step S101is used.

Second Embodiment

In a second embodiment, if a transmission node receives a negativeresponse signal at least N times (N is a natural number of at least 2)consecutively from a reception node, each time the negative responsesignal is received in the at least N times, a set retransmissioninterval value is updated by a value obtained by adding a predeterminedadditional value to the set retransmission interval value. Acommunication apparatus serving as the reception node of the secondembodiment is identical to the communication apparatus 20 serving as thereception node of the first embodiment, and thus the explanation thereofis omitted. Moreover, the basic configuration of a communicationapparatus serving as the transmission node of the second embodiment isidentical to the communication apparatus 10 serving as the transmissionnode of the first embodiment, and thus the basic configuration will bediscussed in accordance with FIG. 1.

The Configuration of the Transmission Node

FIG. 6 is a block diagram showing an example of the communicationcontrol unit of the transmission node according to the secondembodiment. In FIG. 6, a communication control unit 12 in acommunication apparatus 10 serving as the transmission node of thesecond embodiment includes a communication control processing unit 112Aand a calculating unit 112D.

When receiving a positive response signal from a receiving unit 13, thecommunication control processing unit 112A outputs “positive responsecalculation instruction” to the calculating unit 112D. The calculatingunit 112D calculates “updated value” in response to “positive responsecalculation instruction”.

When receiving the negative response signal from a receiving unit 13,like the communication control processing unit 12A of the firstembodiment, the communication control processing unit 112A performsprocessing for retransmission, clearing of a counter 12C, and clearingand starting of a timer 12B. When receiving the negative response signalfrom the receiving unit 13, the communication control processing unit112A further outputs “negative response calculation instruction” to thecalculating unit 112D. The calculating unit 112D calculates “updatedvalue” in response to “negative response calculation instruction.”

When receiving the positive response calculation instruction from thecommunication control processing unit 112A, the calculating unit 112Dacquires the timer value of the timer 12B and the count value of thecounter 12C at the time of reception and calculates “updated value”according to the acquired timer value and count value. An updating unit15 updates the set retransmission interval value according to thecalculated updated value.

For example, when receiving the positive response calculationinstruction, the calculating unit 112D calculates “updated value”according to the following equation (2):

Updated value=timer value+set retransmission interval value×countvalue−predetermined subtraction value α  (2)

When receiving the negative response calculation instruction from thecommunication control processing unit 112A, the calculating unit 112Dacquires the set retransmission interval value with reference to amemory unit 14 and adds a predetermined additional value β to the setretransmission interval value, thereby calculating “updated value. Inother words, when receiving the negative response calculationinstruction from the communication control processing unit 112A, thecalculating unit 112D calculates “updated value” according to thefollowing equation (3):

Updated value=set retransmission interval value+predetermined additionalvalue β  (3)

In this case, the calculating unit 112D may calculate “updated value”upon the reception of the negative response calculation instruction ifit is decided that the count value acquired from the counter 12C is atleast N (N is a natural number of at least 2). If the count value issmaller than N, the calculating unit 112D may not calculate “updatedvalue”.

The predetermined subtraction value α and the predetermined additionalvalue β may be stored in the memory (not shown) of the calculating unit112D or in the memory unit 14.

Operation Example of the Transmission Node

The operations of the communication apparatus 10 configured thus will hedescribed below, the communication apparatus 10 serving as thetransmission node of the second embodiment. FIG. 7 is a flowchartshowing an example of the operations the transmission node according tothe second embodiment.

The communication control unit 12 in the communication apparatus 10serving as the transmission node of the second embodiment performs thesame processing in steps S401 to S405 as in steps S101 to S105 shown inFIG. 3.

If the negative response signal is received (Step S405 YES), thecommunication control unit 12 of the second embodiment increments thecount value of the counter 12C (Step S406).

Subsequently, the communication control unit 12 of the second embodimentdecides whether the count value of the counter 12C is at least N (N is anatural number of at least 2) or not (Step S407). If the count value isat least N (Step S407 YES), an updated value upon the negative responseis calculated according to equation (3) (Step S408).

After that, the updating unit 15 updates the set retransmission intervalvalue stored in the memory unit 14, according to “updated value”calculated by the communication control unit 12 (Step S409). If thecount value of the counter 12C is smaller than N (Step S407 NO), stepsS408 and S409 are skipped and then the processing step advances to stepS410.

Subsequently, the communication control unit 12 of the second embodimentdecides whether the measured value of the timer 12B has reached the setretransmission interval value or not (Step S410). The decision in stepS410 is repeated until the measured value of the timer 12B reaches theset retransmission interval value (Step S410 NO).

If the measured value of the timer 12B has reached the setretransmission interval value (Step S410 YES), the communication controlunit 12 of the second embodiment clears the timer value of the timer 12B(Step S411). After that, the communication control unit 12 of the secondembodiment outputs a retransmission instruction to a transmitting unit11 to retransmit a packet (Step S412). The processing step then returnsto step S403.

When receiving the positive response signal (Step S404 YES), thecommunication control unit 12 of the second embodiment calculates anupdated value upon the positive response according to, for example,equation (2) (Step S413). Subsequently, the updating unit 15 updates theset retransmission interval value stored in the memory unit 14,according to the updated value calculated by the communication controlunit 12 (Step S414). The communication control unit 12 of the secondembodiment then clears the measured value of the timer 12B (Step S415)and the count value of the counter 12C (Step S416).

The processing steps from S402 to S415 are repeated until a series ofpackets has been completely transmitted (Step S417 NO). When the seriesof packets to be transmitted has been completely transmitted (Step S417YES) the processing flow in FIG. 7 is ended.

As described above, in the communication apparatus 10 serving as thetransmission node of the second embodiment, if the communication controlunit 12 receives the negative response signal at least N times (N is anatural number of at least 2) consecutively, each time the negativeresponse signal received in the at least N times, the updating unit 15updates the set retransmission interval value according to a valueobtained by adding the predetermined additional value β to the setretransmission interval value.

The configuration of the communication apparatus 10 sets thepredetermined additional value β at a proper value, thereby preventingthe set retransmission interval value from excessively increasing evenduring repeated retransmission. Moreover, a fine adjustment can becontinued using the predetermined additional value β, thereby settingthe retransmission interval value at a more proper value. In this case,N is a natural number of at least 2 but is not particularly limited.Thus, N may be 1.

In the communication apparatus 10 of the second embodiment, if thecommunication control unit 12 receives the positive response signal, thecalculating unit 112D calculates a time from the transmission of a firstsignal to the reception of the positive response signal corresponding tothe first signal, and then the calculating unit 112D calculates anupdated value by subtracting the predetermined subtraction value α fromthe calculated time. The updating unit 15 then updates the setretransmission interval value according to the updated value.

According to the configuration of the communication apparatus 10, evenif an excessively large value is calculated as an updated value upon anegative response, the updated value can be corrected to a proper value.If the positive response signal is repeated, a smaller updated value iscalculated upon a positive response, thereby setting the retransmissioninterval value for a proper communication environment.

Another Application Example

In the above explanation, the signal to be transmitted is a packet, thepositive response signal is an ACK signal, and the negative responsesignal is a NACK signal. The present invention is not limited to thisapplication example. As in <Another application example> of the firstembodiment, a communication system 1 of the second embodiment may beapplied to a USB-compliant system (Universal Serial Bus).

If the flowchart of FIG. 7 is applied to the transmission node of thecommunication system 1 compliant with the USB (Universal Serial Bus)standard, the need for processing in step S417 is eliminated and thestep of transmitting the ACK response (LPMA) is added instead. Thisflowchart is implemented in each section. In the first section, theretransmission interval value is set at an initial value in step S401.In the subsequent section, the retransmission interval value updated inthe previous section in step S401 is used.

Third Embodiment

A third embodiment relates to a USB-compliant system (Universal SerialBus).

As described in <Another application example> of the first embodiment,if the signal to be transmitted according to the first embodiment is apacket, control on a retransmission interval is also applicable to aUSB-compliant system (Universal Serial Bus) substantially as it is.However, the USB-compliant system (Universal Serial Bus) may have aunique signal transmission status. Thus, in the third embodiment,retransmission interval control will be described in consideration of asignal transmission status specific to a USB-compliant system (UniversalSerial Bus).

A communication apparatus serving as the reception node of the thirdembodiment is identical to the communication apparatus 20 serving as thereception node of the first embodiment and thus the explanation thereofis omitted. Moreover, the basic configuration of a communicationapparatus serving as the transmission node of the third embodiment isidentical to that of the communication apparatus 10 serving as thetransmission node of the first embodiment and thus the basicconfiguration will be discussed with reference to FIG. 1.

The Configuration of the Transmission Node

FIG. 8 is a block diagram showing an example of the communicationcontrol unit of the transmission node according to the third embodiment.In FIG. 8, a communication control unit 12 in a communication apparatus10 serving as the transmission node of the third embodiment includes acommunication control processing unit 212A.

The communication control processing unit 212A outputs “stopinstruction” to a timer 12B if it is decided that “USB data packettransmission condition (hereinafter will be simply referred to as“transmission condition”)” is satisfied. When receiving the stopinstruction, the timer 12B temporarily stops a time measurement.

The communication control processing unit 212A outputs “restartinstruction” to the timer 12B if it is decided that “USB data packettransmission completion condition (hereinafter will be simply referredto as “transmission completion condition”)” is satisfied. When receivingthe restart instruction, the timer 12B restarts the temporarily stoppedtime measurement.

“USB data packet transmission condition” indicates that a USB datapacket needs to be transferred or is being transferred. “USB data packettransmission completion condition” indicates that the transfer of a USBdata packet is completed.

When “transmission condition” is satisfied, the communication controlprocessing unit 212A temporarily stops the time measurement of the timer12B, whereas when “transmission completion condition” is satisfied, thecommunication control processing unit 212A restarts the time measurementof the timer 12B. This can subtract a time during which the transmissionof a USB data packet prevents retransmission of a low-power consumptionstate transition request (LGO_U1/LGO_U2) (that is, the retransmission ofa transition request is held on standby), from the updated value of aretransmission interval value calculated by a calculating unit 12D.

Operation Example of the Transmission Node

The operations of the communication apparatus 10 configured thus will bedescribe below, the communication apparatus 10 serving as thetransmission node of the third embodiment. FIG. 9 is a flowchart showingan example of the operations of the transmission node according to thethird embodiment.

The communication control unit 12 in the communication apparatus 10serving as the transmission node of the third embodiment performs thesame processing in steps S501 to S505 as in steps S101 to S105 shown inFIG. 3. A signal to be transmitted is a low-power consumption statetransition request (LGO_U1/LGO_U2), a positive response signal is an ACKsignal (LAU), and a negative response signal is a NACK signal (LXU).

If the negative response signal is received (Step S505 YES) thecommunication control unit 12 of the third embodiment decides whether“transmission condition” is satisfied or not, that is, whether a USBdata packet needs to be transferred or is being transferred (Step S506).

If “transmission condition” is satisfied (Step S506 YES), thecommunication control unit 12 of the third embodiment stops the timemeasurement of the timer 12B (Step S507).

Subsequently, the communication control unit 12 of the third embodimentdecides whether “transmission completion condition” is satisfied or not(Step S508). The decision is repeated until “transmission completioncondition” is satisfied (Step S508 NO).

If “transmission completion condition” is satisfied (Step S508 YES), thecommunication control unit 12 of the third embodiment restarts the timemeasurement of the timer 12B (Step S509). The processing step thenadvances to step S510. If “transmission condition” is not satisfied(Step S506 NO), steps S507 to S509 are skipped and then the processingstep advances to step S510.

Processing in steps S510 to S513 is identical to that steps S106 to S109in FIG. 3. If it is decided in step S510 that the measured value of thetimer has not reached the set retransmission interval value (Step S510NO), the processing step return to step S506. Moreover, the low-powerconsumption state transition request (LGO_U1/LGO_U2) is to beretransmitted in step S513. Processing in steps S514 to S517 isidentical to that of steps S110 to S113 in FIG. 3.

In this case, the communication control unit 12 of the third embodimenttransmits an ACK response (LPMA), which is specific to the USB standard(Step S518).

The flowchart of FIG. 9 is implemented in each section (e.g., sections Cand D). In the first section (e.g., the section C, which will bediscussed later), the retransmission interval value is set at an initialvalue in step S501. In the subsequent section (e.g., the section D,which will be discussed later), the retransmission interval valueupdated in the previous section (e.g., the section C, which will bediscussed later) in step S501 is used.

FIG. 10 is a sequence showing an example of the operations of thecommunication system according to the third embodiment. In FIG. 10, forexample, one of the communication apparatus 10 and the communicationapparatus 20 is a host, whereas the other is a device. Moreover, in FIG.10, the section C is a section (sequence) where the communicationapparatus 10 changed a state used for communications with thecommunication apparatus 20, and the section D is a section (sequence)where the communication apparatus 10 changed a state used forcommunications with the communication apparatus 20 at anotheropportunity after the section C. For example, in the section C, thecommunication apparatus 10 and the communication apparatus 20 arecoupled to transmit a low-power consumption state transition request(LGO_U1/LGO_U2) for the first time and the retransmission interval valueapproaches closest to an optimal value.

At the beginning of the section C, the power consumption states of thecommunication apparatus 10 and the communication apparatus 20 are bothdesignated as a U0 state. The communication apparatus 10 transmits thelow-power consumption state transition request (LGO_U1/LGO_U2) to thecommunication apparatus 20 (Step S601). At this point, the measurementof the timer 12B is started.

In this case, the communication apparatus 20 having received thelow-power consumption state transition request transmits the NACK signal(LXU) (Step S602).

Subsequently, the transmission of USB data packets is started betweenthe communication apparatus 10 and the communication apparatus 20 (StepS603). At this point, as described above, the time measurement of thetimer 12B is temporarily stopped during the transmission of USB datapackets. At the completion of the transmission of USB data packets instep S603, the time measurement of the timer 12B is restarted.

At the completion of the transmission of USB data packets, thecommunication apparatus 10 retransmits the low-power consumption statetransition request after a lapse of the set retransmission intervalvalue from the transmission of the low-power consumption statetransition request in step S301 (Step S604). At this point, the measuredvalue of the timer 12B is cleared and then the timer 12B restarts ameasurement; meanwhile, the count value of the counter 12C is furtherincremented.

The communication apparatus 20 having received the retransmittedlow-power consumption state transition request transmits the ACK signal(LAU) to the communication apparatus 10 (Step S605).

When receiving the ACK signal (LAU) from the communication apparatus 20,the communication apparatus 10 acquires the measured value of the timer12B at this point and then terminates the measurement of the timer 12B.Moreover, the communication apparatus 10 acquires the count value of thecounter 12C and the set retransmission interval value at this point. Inthis case, the communication apparatus 10 and the communicationapparatus 20 are coupled to transmit the low-power consumption statetransition request (LGO_U1/LGO_U2) for the first time in the section Cand thus the acquired set retransmission interval value is equal to theinitial value. The communication apparatus 10 substitutes these valuesin Equation (1) to calculate an updated value and then updates the setretransmission interval value according to the calculated updated value.

The communication apparatus 10 then transmits the ACK response (LPMA) tothe communication apparatus 20 (Step S606) and the communicationapparatus 20 receives the ACK response (LPMA). This changes the powerconsumption states of the communication apparatus 10 and thecommunication apparatus 20 to a state indicated by the low-powerconsumption state transition request.

In steps S607 to S612 of the section D, the same processing is performedas in steps S601 to S606. In this case, a time interval between thetransmission of the transition request in step S607 and theretransmission of the transition request in step S610 is longer than orequal to the retransmission interval value updated in the section C.

As described above, the low-power consumption state transition request(LGO_U1/LGO_U2) is transmitted between the transmission period of USBdata packets. In this case, when the NACK signal (LXU) is returned inresponse to the low-power consumption state transition request(LGO_U1/LGO_U2), whether to retransmit the low-power consumption statetransition request (LGO_U1/LGO_U2) is decided depending on the necessityfor the transmission USB data packets. If USB data packets need to betransmitted, the low-power consumption state transition request(LGO_U1/LGO_U2) is retransmitted after the completion of thetransmission of USB data packets. If USB data packets are transmittedbetween the retransmission flows of the low-power consumption statetransition request (LGO_U1/LGO_U2), a continuous time measurement of thetimer 12B may lead to calculation of an excessively large retransmissioninterval value. Thus, the timer 12B is stopped during the transmissionof USB data packets.

As described above, according to the third embodiment, the updating unit15 in the communication apparatus 10 serving as the transmission node ofthe second embodiment updates the set retransmission interval valuebased on a time determined as follows: the time is determined bysubtracting the transmission time of USB data packets between thetransmission of the transition request and the reception of the ACKsignal corresponding to the transition request, from a time from thetransmission of the transition request (i.e., the low-power consumptionstate transition request) to the reception of the ACK signalcorresponding to the transition request.

The configuration of the communication apparatus 10 can prevent the setretransmission interval value from excessively increasing if USB datapackets are transmitted between the retransmission flows of thetransition request.

Another Embodiment

(1) In the first embodiment, the set retransmission interval value isused each time a packet is retransmitted. The present invention is notlimited to the set retransmission interval value. For example, in thefirst retransmission of a packet, a time interval from the firsttransmission of the packet to the first retransmission of the packet maybe set longer than or equal to the set retransmission interval value. Inthe second retransmission or later, a packet may be retransmittedimmediately after preparation for retransmission.(2) In the first and third embodiments, during repeated retransmissionof a signal to be transmitted, the retransmission is controlledaccording to the retransmission interval value calculated in thetransmission of the previous signal to be transmitted. The presentinvention is not limited to the retransmission control. For example, theset retransmission interval values in the memory unit 14 maybe appliedto repeated retransmission based on a predetermined retransmissioninterval-value application pattern, the set retransmission intervalvalues including a first set retransmission interval value that iscontinuously updated and a second set retransmission interval value thatis a fixed interval value as described in the first and thirdembodiments the For example, the second set retransmission intervalvalue set at a sufficiently small value may be used for the firstretransmission, whereas the first set retransmission interval valuemaybe applied to the second retransmission or later.(3) In the first to third embodiments, the communication apparatus 10 isconfigured as a transmission node, whereas the communication apparatus20 is configured as a reception node. Obviously, both of thecommunication apparatus 10 and the communication apparatus 20 may beconfigured as a transmission node and a reception node.(4) For clarification of the explanation, the description and drawingsare optionally omitted and simplified. Moreover, elements illustrated asfunctional blocks for various kinds of processing may include hardwaresuch as a CPU, a memory, and other circuits and are implemented byprograms loaded in the memory. Thus, a person skilled in the art couldunderstand that these functional blocks can be implemented in variousforms including hardware alone, software alone, or a combination of thehardware and software. The present invention is not limited to the formsof the functional blocks.

Furthermore, the programs are stored using various types ofnon-transitory computer readable media and can be supplied to acomputer. The non-transitory computer readable media include varioustypes of tangible storage media. The non-transitory computer readablemedia include a magnetic recording medium (e.g., a flexible disk, amagnetic tape, and a hard disk drive) a magneto-optical recording medium(e.g., a magneto-optical disk), a CD-ROM (Read Only Memory), CD-R, aCD-R/W, a semiconductor memory (e.g., a mask ROM, a PROM (ProgrammableROM), an EPROM (Erasable PROM), a flash ROM, and a RAM (Random AccessMemory)). The programs may be supplied to a computer via various typesof non-transitory computer readable media. The non-transitory computerreadable media include an electrical signal, an optical signal, and anelectromagnetic wave. The non-transitory computer readable media cansupply programs to a computer through wire communication channels suchas an electric wire and an optical fiber or radio channels.

The invention made by the inventors was specifically described accordingto the embodiments. Obviously, the present invention is not limited tothe foregoing embodiments and can be changed in various manners withoutdeparting from the scope of the invention.

What is claimed is:
 1. A communication apparatus comprising: a memoryunit where a retransmission interval value is stored; a communicationcontrol unit that transmits a first signal and receives a responsesignal corresponding to the first signal from a receiver, thecommunication control unit retransmitting the first signal at a timeinterval longer than or equal to the retransmission interval value afterthe transmission of the first signal if the received response signal isa negative response signal, and an updating unit that updates the storedretransmission interval value according to a time from the transmissionof the first signal to the reception of the positive response signalcorresponding to the first signal.
 2. The communication apparatusaccording to claim 1, wherein if the communication control unit receivesthe negative response signal at least N times (N is a natural number ofat least 2) consecutively, each time the negative response signal isreceived in the at least N times, the updating unit updates the storedretransmission interval value according to a value obtained by adding apredetermined additional value to the stored retransmission intervalvalue.
 3. The communication apparatus according to claim 1, wherein ifthe communication control unit receives the positive response signal,the updating unit updates the stored retransmission interval valueaccording to a value obtained by subtracting a predetermined subtractionvalue from a time from the transmission of the first signal to thereception of the positive response signal corresponding to the firstsignal.
 4. The communication apparatus according to claim 1, wherein thefirst signal is a transition request signal to a low power consumptionstate defined by a USB (Universal Serial Bus) standard, wherein theresponse signal is a response signal indicating whether to accept atransition in response to the transition request signal, and wherein theupdating unit updates the stored retransmission interval value based ona time determined by subtracting a transmission time of a USB datapacket between the transmission of the first signal and the reception ofthe positive response signal corresponding to the first signal, from atime from the transmission of the first signal to the reception of thepositive response signal corresponding to the first signal.
 5. Thecommunication apparatus according to claim 1, wherein if thecommunication control unit receives the positive response signalcorresponding to the first signal, the communication control unittransmits a second signal subsequent to the first signal to the receiverafter a predetermined time from the reception of the positive responsesignal.
 6. A communication method comprising the steps of: transmittinga first signal and receiving a response signal corresponding to thefirst signal from a receiver; retransmitting the first signal at a timeinterval longer than or equal to a retransmission interval value storedin a memory unit from the transmission of the first signal if thereceived response signal is a negative response signal, and updating thestored retransmission interval value based on a time from thetransmission of the first signal to the reception of the positiveresponse signal corresponding to the first signal.
 7. The communicationmethod according to claim 6, wherein if the negative response signal isreceived at least N times (N is a natural number of at least 2)consecutively, each time the negative response signal is received in theat least N times, the stored retransmission interval value is furtherupdated according to a value obtained by adding a predeterminedadditional value to the stored retransmission interval value.
 8. Thecommunication method according to claim 6, wherein during updating ofthe stored retransmission interval value, if the positive responsesignal is received, the stored retransmission interval value is updatedaccording to a value obtained by subtracting a predetermined subtractionvalue from a time from the transmission of the first signal to thereception of the positive response signal corresponding to the firstsignal.
 9. The communication method according to claim 6, wherein thefirst signal is a transition request signal to a low power consumptionstate defined by a USB (Universal Serial Bus) standard, wherein theresponse signal is a response signal indicating whether to accept atransition in response to the transition request signal, and wherein thestored retransmission interval value is updated based on a timedetermined by subtracting a transmission time of a USB data packetbetween the transmission of the first signal and the reception of thepositive response signal corresponding to the first signal, from a timefrom the transmission of the first signal to the reception of thepositive response signal corresponding to the first signal.
 10. Thecommunication method according to claim 6, wherein if the positiveresponse signal corresponding to the first signal is received, a secondsignal subsequent to the first signal is transmitted to the receiverafter a predetermined time from the reception of the positive responsesignal.